Just how wide is New York City's income gap?

Closing New York City's income gap is at the top of new Mayor Bill de Blasio's agenda.

In his inaugural address, the city's first Democratic mayor in two decades said: "We are called to put an end to economic and social inequalities that threaten to unravel the city we love."

But that will be a Herculean lift. A new report from the City University of New York's Graduate Center shows that the gap has become a canyon since 1990. Median income has soared for those at the top, but it has stagnated on the lower rungs.

The wealthy are also taking a larger piece of the income pie, while the middle class is losing ground and the poor are stuck in place.

In fact, the rich are the only ones who have seen their share of the city's income grow.

The report also found that whites control more than half the income in the city, though they make up just over one-third of the population.

Latinos and blacks lag behind in terms of income earned compared to their share of the population.

First up on the new mayor's agenda? Raising taxes on the rich to pay for early education and after-school programs. Economic mobility experts point to education as one way to narrow income inequality.

Tami Luhby is a senior writer at CNNMoney and covers income inequality, state fiscal problems, unemployment, housing policy and other economic issues. Luhby previously covered personal finance for Newsday and banking for Crain's New York Business.